Actually, laws banning violent video games have been ruled unconstitutional, see Brown v. Entertainment Merchants Association[1]. The laws weren't that commonplace before the Supreme Court ruling, either.
I am as skeptical about laws regulating video games as you seem to be, but laws about video game violence in the United States are hardly 'strict.' After all, the agency that rates video games, the ESRB, is run by the industry itself. And I am unaware of any legal obligation to take part in the ESRB.
Finally, the U.S. doesn't use PEGI ratings, a group of nine European nations do. But you are right in saying Poland has liberal laws — game publishers do not have to have their games rated by PEGI.
USA - strict laws against violence in games (PEGI ratings etc), liberal gun control, 4.8 intentional homicides per 100 000 citizens
Poland - liberal law regarding violence in games, strict gun control, 1.1 intentional homicides per 100 000 citizens
Source: http://en.wikipedia.org/wiki/List_of_countries_by_intentiona...